Known containers made of tin or multicolored sheet metal, glass or else ceramic, are increasingly being replaced by containers made of plastic. In the meantime, primarily plastic containers can be used for example, for the packaging of fluid substances, for example beverages, household products, care products, cosmetics, etc. The low weight and the lower costs can play a significant role in this substitution. The use of recyclable plastic materials and the overall total energy balance in their production can also contribute to promoting the acceptance of plastic containers, for example plastic bottles, in consumers.
The production of plastic containers, for example plastic bottles, for example made of polyethylene or polypropylene, has been carried out in an extrusion-blow-molding method, for example in a plastic hose blow method. In this method, a plastic hose is extruded with an extrusion head, introduced into the mold cavity of a blow mold tool, inflated by overpressure, cooled and demolded. The inflation of a plastic hose section introduced into the blow mold cavity can be carried out with a calibrating blow pin, which is inserted through an opening of the blow mold cavity. On the one hand, the calibrating blow pin provides a function of introducing air into the plastic hose, so that the latter is formed according to the blow mold cavity. On the other hand, the calibrating blow pin is also used for defined inside forming (calibration) of the neck of the plastic container, in which the pour opening is provided. This shaping function of the calibrating pin includes (e.g., consists of) a defined determination of the inside diameter of the neck. To this end, the calibrating blow pin is inserted through the opening of the closed blow mold tool into the hose section. Thereby, excess plastic material is axially displaced, and the inside diameter of the neck is determined with the pour opening.
In the case of pour openings with inside diameters of, for example, approximately 10 mm to approximately 85 mm, this type of calibration has proven to be very practicable, and the desired dimensional accuracy can be achieved without great difficulty.
In the case of smaller inside diameters of for example less than 7 mm, however, a danger can exist that the calibrating blow pin pushes the softened plastic material through the opening of the blow mold tool during axial advance, and it thus results in a defective design of the neck. This can occur when, for example, there is no plastic material available from the adjacent areas above during the axial movement of the calibrating blow pin for the calibration.
In the case of plastic containers, which in addition to the larger pour opening have a smaller pour opening, which is provided, for example, within the plastic container, the calibration can prove to be even more difficult. The smaller pour opening is connected, for example, to another chamber of the plastic container.
In another variant, the smaller pour opening can be an outlet of a metering tube arranged within the plastic container, which tube is to be connected to a metering chamber that is, for example, integrated in a pour attachment, which is attached to the neck of the completed blow-molded plastic container. For the inflation of such plastic containers, double calibrating blow pins can be used, which can be designed in such a way that the pour opening on the neck of the plastic container and that in the second chamber or in the metering tube can be formed at essentially the same time.
While the calibration of the pour opening on the neck can be achieved without great difficulty because of its relatively large inside diameter, the direct calibration of the smaller opening with the double calibrating blow pin can prove to be very difficult. For this reason, the calibration of the smaller opening is carried out within the inflated container by for example, machining such as with spindles, which follows the blow-molding process to achieve the desired dimensional accuracy of, for example, up to ±0.03 mm. The machining can however have a drawback that chips fall into the interior of the container and should be removed again from there.
In the case of a metering tube with a relatively small inside diameter, a danger exists that the chips cannot be completely removed. The latter can then prevent a flow through the metering tube and can result in the plastic container that is produced having to be rejected. Moreover, the machining and the subsequent removal of chips represent involve additional operating steps, which increase the expense for the production of the plastic container.